Current connections designed for double-layer-grids receive linear, structural elements that, most commonly, are either round or square in cross-section. In such grids, the places where plural linear elements are interconnected are known as “nodes”. FIG. 1 illustrates a conventional node connector 2 for square cross-section framing members 3, 4. Note that the adjacent diagonal strut members at 4 the connection reside in different planes. That is, the non-vertical surfaces 5 of each diagonal strut member 4 lie in (or are parallel to) a plane diagonal to the common plane of the adjacent horizontal chord members 3 which is different from the diagonal plane of each other diagonal strut member associated with the connector.
Bolted connections are easily effected using these systems that accommodate square linear, tubular structural elements. The use of a square cross-section for the framing is advantageous since the fabrication of the framing member consists simply of drilling or punching holes at both ends after the member is cut to length. Ball-node systems are designed for the use of round cross-sections (pipes) in double-layer-grids and involve a more expensive design and fabrication process.
A double-layer-grid is understood to be a structure with a horizontal, square grid of framing elements that serve as the top chords and is the top “layer” of the DLG space frame. Similarly, there are the bottom chords with the same square grid that is offset horizontally by one-half the bay width in both directions. This bottom “layer” is also offset downwardly from the top “layer” by a set distance and is held in position by the use of diagonal (strut) framing elements. FIGS. 2, 3 & 4 show a typical double-layer-grid space frame 6, six bays long by five bays wide; an end view of frame 6 is similar to FIG. 4. There are several disadvantages of the connection systems of the prior art when applied to double-layer grids as described with square cross-section framing elements. First, these systems are restricted to square, double-layer-grids only. Second, these systems can only produce flat double-layer grids. Third, contoured (free-form) footprints are difficult to design and construct. Fourth, vertical sidewall and/or end wall framing is difficult to design and construct. These disadvantages are resolved with the DLGC design.